Horizontal fire tube steam generator with water tubes



p 27, 5 E- c. MILLER 2,718,881

HORIZONTAL FIRE TUBE STEAM GENERATOR WITH WATER TUBES Filed Oct. 4, 1951 INVENTOR EARL E 6. MILL E]? I Y MJMW ATTORNEY HORIZONTAL FIRE TUBE STEAM GENERATOR WITH WATER TUBES Earle C. Miller, Worcester, Mass., assignor to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts Application October 4, 1951, Serial No. 249,771

3 Claims. (Cl. 122-104) This invention relates generally to steam generating units and more particularly to apparatus making use of a spreader stoker with a traveling grate.

In firing boilers by use of a spreader stoker, it is common practice to make use of coal having a high percentage of fines. This presents a number of problems, not the least of which is that fines have a tendency to travel with the flow of gases and very often pass out 'of the combustion chamber before being burned. This means a sooty discharge from the stack as Well as poor efficiency. Furthermore, the lean gases from the discharge end of the grate tend to pass directly upward instead of mixing with the main body of gases. The present invention obviates these difficulties by providing a novel arrangement for causing the path of the gases in the furnace to be long enough for combustion of fines to take place and for trapping flyash and the like in order that the discharge from the stack will be clean and advantage may be taken of the principles of flyash reinjection.

It is therefore an outstanding object of the present invention to provide a steam generating unit in which the path of the gases is such as to bring about better combustion of fines and better collection of flyash.

A further object of this invention is the provision of a steam generating unit making use of a spreader stoker in conjunction with a traveling grate and a two-pass, fire-tube boiler and utilizing to advantage the principles of flyash reinjection.

Furthermore, it is an object of this invention to provide a furnace for a two-pass, fire-tube boiler in which the gases of combustion make two horizontal passes through the length of the furnace before entering the boiler tubes. It is a further object of the invention to provide a novel baffiing arrangement for a spreader socket furnace.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by referring to the following description taken in connection with the accompanying drawings forming part thereof, in which:

Figure 1 is a vertical sectional view of the steam generating unit of the invention, and

Figure 2 is a sectional view of a portion of the invention taken on the line 2-2 of Figure 1.

Referring to Figure l, which best shows the general features of the invention, the steam generating unit, generally designated 10, is shown as comprising a furnace 11 and a two-pass, water tube boiler 12. The furnace 11 comprises a back wall 13, a front wall 14, and side walls 15, all supported on a floor 16. A traveling grate 17 is shown mounted in the lower portion of the furnace adjacent the floor 16 and a spreader stoker 18 of the mechanical type shown in the Miller Patent 2,538,944 is mounted in the front wall 11 so as to spread fuel over the surface of the grate in the well-known manner. In

nited States Patent 2,718,881 Patented Sept. 27, 1955 the preferred embodiment, the traveling grate is driven so that its upper surface moves toward the front wall. An ash pit 19 is provided in the floor at the forward end of the traveling grate for receiving consumed fuel therefrom. Another ash pit 20 is provided at the rear end of the grate for receiving siftings that pass through the uppermost part of the grate, fall on the lower part of the grate and are thus carried to the rearward part of the grate and dumped. The front wall of the furnace is provided with the usual door 21 and has an offset refractory portion 22 overlying the forward end of the grate 17. In the specific embodiment shown, the rear wall of the furnace is formed in part by an extension 23 of the boiler 12 and the front wall is formed in part by an extension 24. A passage 25 is formed through the extension 24 for the operation of the spreader stoker 18. A refractory bridge wall 26 is provided rearwardly of the furnace and overlying the rear end of the grate; the bridge wall is provided with a stepped surface 27 which is inclined upwardly and rearwardly of the furnace. The arch wall is supported by a brace 28 and is connected to the back Wall by a horizontal web 29 of refractory.

The boiler 12 comprises a lower set of horizontal fire tubes 30 and an upper set of horizontal fire tubes 31. Entrance to the tubes 30 is brought about at the front end thereof by the provision of a curved recess 32. The rear ends of the tubes 30 and 31 are joined by a housing 33 which has a flyash hopper 34 at the bottom thereof; the hopper 34 is joined to a conduit 35 which extends vertically down the back wall of the furnace, bends abruptly and extends generally horizontally into the furnace through the rear wall 13, the web 29, and the arch wall 26. The conduit 35 opens on the surface 27 of the bridge wall. An ejector nozzle 36 is introduced into the conduit 35 at the bend and this nozzle is attached to a source of steam or air under pressure. The forward ends of the upper boiler tubes 31 open into the flue 37.

A row of water tubes 38 extend longitudinally of the furnace from the extension 23 of the boiler on a level with the arch wall to the extension 24 above the spreader stoker; thus, the water tubes 38 extend upwardly and forwardly through the furnace. A bafiie 39 is supported by and extends between the row of tubes 38. This baffle extends transversely across the furnace and along the tubes 38 from the area of their attachment to the extension 24 of the boiler to a line about half way between the front and rear walls of the furnace. The rearward edge, denoted by the reference character 40, is in a somewhat critical relation to the surface 27 of the bridge wall; it is spaced upwardly and forwardly of the surface 27 and the space therebetween is relatively constructed as compared with other gas-flow passages in the unit.

Referring next to Figure 2, it can be seen that the bathe 35! is made up of a number of sections 41 having cyiindrical recesses in their vertical surfaces for embracing the tubes 38. The sections fit together to form a gastight wall across the furnace and, in the preferred embodiment, they completely enclose and cover the upper, forward halves of the tubes.

The operation of the steam generating unit is as follows: the fuel is delivered to the spreader stoker 18 in the well-known manner and is thrown onto the traveling grate 17 at the rearward portion thereof. The fuel is subjected to the various stages of combustion in passing ice from the back to the front of the grate and is more or less the fuel which eventually burns in the combustion chamber; the gases will also contain fine particles of fuel which never reach the surface of the grate, but remain suspended in the gas flow after being thrown therein by the spreader stoker. It is these fine particles that We are primarily concerned with here. The gases flow upwardly until they contact the bafiie 39 at which time they are forced to flow downwardly and rearwardly along the underside of the baffle. The gases then flow through the space or throat between the edge 40 of the baffle and the surface 27 of the bridge wall. The gases, because of their inertia continue moving generally horizontally along and through the bare portions of the water tubes 38. They impinge against the back wall of the furnace and the extension 23 of the boiler and move upwardly therealong. The reversal of movement of the gases causes some of the solids to be thrown out of the flow onto the web 29. The gases move upwardly along the back wall and are forced to move forwardly and generally horizontally by the bottom surface of the boiler proper. They then move forwardly over the top surface of the baflie 39 and are admitted to the lower tubes 30 of the boiler through the recess 32. The gases pass rearwardly through the tubes 30 and into the housing 33. From the housing 3.3 the gases enter the upper tubes 31 and pass forwardly therethrough into the flue 37. The gases during their passage give heat to the water in the tubes 38 and to the water surrounding the tubes 30 and 31 whereby steam is generated. When the gases leave the tubes 30 and are reversed in the housing 33 before entering the tubes 31, a considerable amount of fiyash is thrown out of the main stream and collects in the hopper 34'. The ejector nozzle 36 carries the flyash from the hopper 34 through the conduit 35 and reinjects it into the combustion chamber at the surface 27 of the bridge wall. Since this flyash usually contains a high percentage of unburned particles, the efliciency of the unit is improved.

Without the baffle and bridge Wall arrangement shown, the gases would flow to the recess 32 of the boiler by the most direct route. This would result in a very high carry-over of fines and would not give the fine particles sufficient time to burn before the gases were cooled by movement through the boiler tubes. Furthermore, a considerable amount of flyash is removed from the main stream of gas by the reversal at the back. of the furnace. Also, the gases coming from the discharge end of the grate are very lean and should be thoroughly mixed with the main body of gases in order to keep up the efiiciency of the unit and improve the combustion. Without the present arrangement, the lean gases would flow in a segregated stream up the front Wall of the furnace into the recess 32.

While certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions, and changes in the forms and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent 1. A steam generating unit comprising a furnace having forward and rear walls, a horizontal fire-tube boiler having two gas passes mounted in the upper portion of said furnace, the entrance to the first pass of said boiler being adjacent the forward wall of said furnace, a spreader stoker mounted in the forward wall of said furnace, a forwardly-traveling grate mounted in the furnace below the level of said stoker, a bridge wall overlying the rearward end of the grate and having a surface which is inclined rearwardly and upwardly of the furnace, a row of water tubes extending across the furnace from forward wall to rear wall, said row of water tubes being inclined upwardly and forwardly of the fur nace, a baffle extending transversely and rearwardly from the front wall of the furnace and along said row of water tubes to within a short distance of the inclined surface of said bridge wall, a housing joining the rearward ends of the fire-tubes of the boiler, a hopper forming a bottom for said housing for collecting fly-ash, a conduit running from said hopper to the bridge wall and opening in the inclined surface thereof, and an ejector nozzle situated in said conduit through which a gas may be projected to promote flow of fly-ash from the hopper and through the conduit.

2. A steam generating unit comprising a furnace having forward and rear walls, a horizontal fire-tube boiler having two gas passes mounted in the upper portion of said furnace, the entrance to the first gas pass of said boiler being adjacent the forward wall of said furnace, a spreader stoker mounted in the forward wall of said furnace, a traveling grate mounted in the furnace below the said entrance, a refractory bridge wall overlying the rearward end of the grate and having a surface which is inclined so as to face in the general direction of the said entrance, said front and rear walls of the furnace being formed at least in part by water-bearing portions of the boiler, a row of water tubes extending across the furnace and joining the said water-bearing portions of the front and rear Walls, said row of water-tubes extending from above the spreader stoker to a lower portion of the rear wall, a baffle sheathing said row of tubes in the portion thereof overlying the grate and extending along the tubes to within a short distance of the inclined surface of the bridge wall, a housing joining the rearward ends of the boiler fire-tubes, a hopper forming a bottom for said housing and joined to said bridge wall for reinjection of fiyash from the hopper to the restricted passage between the rearward edge of the battle and the inclined surface of the bridge wall.

3. A steam generating unit comprising a furnace having forward and rear walls, a boiler mounted in the upper portion of said furnace, the entrance to a gas pass of said boiler being adjacent the forward wall of said furnace, a spreader stoker mounted in the forward wall of said furnace, a traveling grate mounted in the furnace below the level of said stoker, a bridge wall overlying the rearward end of the grate and having a surface which is inclined rearwardly and upwardly of the furnace, a row of water tubes extending across the furnace from forward wall to rear wall, said row of water tubes being inclined upwardly and forwardly of the furnace, a baffie extending transversely and rearwardly from the front wall of the furnace and along said row of tubes and having a rearward edge situated a short distance from the inclined surface of said bridge wall to form a restricted passage therewith through which the combustion gases pass prior to entering the said gas pass, a hopper underlying a portion of the boiler for collecting unburned fuel from the combustion gases, a conduit running from said hopper to the bridge wall and opening in the inclined surface thereof, and an ejector nozzle situated in said conduit through which a gas may be projected for bringing about flow of the unburned fuel through the conduit from the hopper to the restricted passage between the rearward edge of the bafiie and the inclined surface of the bridgewall.

References Cited in the file of this patent UNITED STATES PATENTS 455,805 Sutclilfe July 14, 1891 951,813 Hawkes Mar. 15, 1910 986,649 Sewall Mar. 14, 1911 1,642,692 Obert Sept. 20, 1927 1,672,413 Holt June 5, 1928 2,386,336 Mosshart Oct. 9, 1945 2,592,701 Jackson Apr. 15, 1952 

